The present invention concerns the making of electronic units including at least one microcircuit which is embedded in a carrier medium and linked to interface elements consisting of a terminal block and/or an antenna, such as integrated circuit cards with or without contacts, also known as smart cards.
The invention also applies, in particular, to electronic labels which are used to identify products and which can be compared with smart cards without contacts.
The present invention concerns more particularly the making of connections between the microcircuit and the interface elements, such as a terminal block and/or antenna.
There are contact smart cards with interface terminal blocks, smart cards without contacts with an antenna housed in the carrier medium and hybrid cards or combicards which have an interface terminal block and an antenna.
There are numerous methods for making smart cards with contacts. Most of these methods are based on assembly of the chip in a sub-set called a micromodule which is assembled using traditional methods.
One method, illustrated in FIG. 1, involves first attaching the chip or microcircuit 20 (xe2x80x9cdie attachxe2x80x9d) which involves gluing a chip 20, cut from a board by sawing, arranging it with its active side with its exit hubs 22 upwards and by sticking the opposite side on a dielectric support plate 28, using a glue which could be conducting, the gluing being done on a printed circuit or film.
Then microcabling or soldering of connections is done (xe2x80x9cwire bondingxe2x80x9d), involving soldering the connection of the exit hubs 22 of the chip 20 with the terminal block of contacts 24 of the printed circuit plate.
Then the case is coated (xe2x80x9cpottingxe2x80x9d), involving protecting the chip 20 and the soldered connection wires 26 using a resin 30 which could be silicone or polyurethane based, for example.
In a variation of this method illustrated in FIG. 2, a peripheral metallic ring 32 is used to rigidify the micromodule around the resin 30.
In another variation of this method (xe2x80x9cflip chipxe2x80x9d), a chip with bumps or protuberances placed with the active side downward is used, the electrical connection being provided either by metallic or polymer bumps or by an anisotropic adhesive.
In other variations, tape automated bonding (TAB) is used, as illustrated in FIG. 3, according to which the chip 34 is glued using an anisotropic glue 36 and the various contacts of the film 38 are soldered by thermocompression on the chip 34 which has bumps 39.
There are also methods for making smart cards with contacts without using micromodules. One method is based on using screen printing to form contacts and to provide chip interconnections.
Another method involves metallisation in three dimensions of the body of the card, followed by transfer of the chip using classic technology (gluing plus microcabling) or by the xe2x80x9cflip chipxe2x80x9d technique described above.
In the methods which use a micromodules, the associated costs are limited by the price of the film. In addition, it is often necessary, after the encapsulation operation, to mill the resin to reduce the thickness of the unit. This operation is difficult because the resin is polymerised and thus very rigid. The milling is the main cause of production rejects.
In the first method without micromodules described above, this latter is on the surface and thus subject to exterior stresses, greatly increasing the associated cost. For the second method without micromodules the number of steps is high which also increases the cost.
This technology would therefore not be suitable for making large chip cards.
There are two large families of methods for making smart cards without contacts. The first uses an antenna made by winding which is either soldered on a micromodule containing the chip, or directly on a chip with bumps. Such a technique can only be used for chips with simple operation.
The second family uses a xe2x80x9cflatxe2x80x9d antenna which can be in the form of a rectangular peripheral spiral or any other appropriate form. Such an antenna can be made by photogravure, mechanical cutting, stamp printing, screen printing, or offset printing with a conducting ink. The chip is then transferred to the antenna using the xe2x80x9cflip-chipxe2x80x9d technique or a classic technique.
In these methods for making smart cards without contacts, micromodule manufacturing is used which, as mentioned above, involves numerous steps for assembling the chip and implies substantial costs, or the xe2x80x9cflip-chipxe2x80x9d technique for which the pace is limited and the installation costs particularly high.
The methods for hybrid smart cards combine the disadvantages previously mentioned for smart cards both with and without contacts.
The basic purpose of the invention is to provide a method for making connections between a microcircuit and the interface elements in an electronic unit (such as a smart card) including at least one microcircuit which is embedded in a carrier medium and which includes exit hubs linked to interface elements including a terminal block and/or an antenna which do not have the above mentioned disadvantages and which make it possible in particular to reduce the cost and percentage of production rejects without making micromodules.
The method according to the invention is remarkable in that it involves depositing, using a syringe or similar device, of a drop of a low-viscosity conducting substance between each exit hub and the corresponding interface element, the said conducting substance acting by polymerisation, including conducting charges and remaining flexible after polymerisation.
This method makes it possible to eliminate the making of micromodules and to reduce the number of production steps.
In addition, flexible connections are obtained whereas the connections of the known type are rigid or semi-rigid and this sharply reduces the rate of production rejects.
Advantageously, the terminal block is also made by depositing a low-viscosity conducting substance.
This makes it possible to further simplify the method with the making of the terminal block and its connections done in a single operation.
Advantageously, the antenna is also made by depositing a low-viscosity conducting substance.
This makes it possible to simplify the production and to improve the antenna performance.
The substance should preferably be a polymer resin charged with conducting or intrinsically conducting particles.